Agatha Shelley is a pen name Fern uses in "Fern and Persimmony Glitchet" after a letter by Persimmony Glitchet advises her never to use her real name when publishing. As Agatha Shelley Fern writes Happy Happenings and A Terrible Twist, both published in the Lakewood Elementary Reader.
The name is a combination of Agatha Christie and Mary Shelley, two famous writers that Fern admires.